The Data Core provides a central resource to the ADCS consortium for expertise in the design, management, quality control and analysis of Alzheimer's disease clinical trials. The biostatistical responsibilities of the Data Core include: collaborating on the experimental design of each protocol; developing and generating the randomization sequences for each trial; performing preliminary and final statistical analysis on trial results; the preparation of reports and publication; and developing new statistical methodology. All ADCS clinical trial data is managed through the Data Core. Every aspect of the data collection process, including forms design and printing, maintaining centralized patient files, and generating special purpose and routine statistical reports on accumulating data, is coordinated through the data management operation of the Data Core. The Data Core computing environment consists of approximately 50 workstations connected in a client-server architecture, using a TCP/IP local area network (LAN) with 4 servers (web, file, data, and mail). The network is secured behind a firewall. Data management is conducted through the Oracle relational database management system. The quality assurance program of the Data Core is extensive. At its center is the clinical and computerized monitoring of the data, but it extends to cover training, study initiation, sub-contractor liaison, supply procurement, document (training manuals, manuals of operation, newsletters, etc.) and instrument development. The Data Core coordinates a clinical monitoring program through which all ADCS data forms are reviewed on-site by highly trained monitors. Computerized edit checking is done both at the time of entry and longitudinally. The Data Core maintains public and private web sites in support of ADCS activities.